The present invention relates to a stringed instrument, such as a guitar, employing an improved electrical pickup.
Stringed instruments generate sound by the controlled vibration of the strings. The latter vibrate at different frequencies to generate notes of varying pitch. On most acoustical instruments, the strings are placed on or near a hollow sound chamber or sound board which combines and amplifies the sound waves to create the full rich tones that music lovers have enjoyed for centuries.
This century, however, has seen the rise of electrical musical instruments, most notably the electric guitar and the electric bass. On such instruments, the function of the hollow sound chamber is replaced by an electric power amplifier. Electrical transducers called "pickups" are placed on the instrument to sense the vibration of the strings and convert the vibrational energy into an electrical signal. This signal is then boosted by the amplifier and broadcast over a loud speaker. The electrical pickup is thus a key component: the more accurately the output signal follows the vibration of the strings, the more true will be the sound reproduced by the loudspeaker.
Most stringed instruments, such as guitars, have more than one string. It is desirable that in order to more faithfully reproduce the sound of the instrument, the vibration of each string should be separately transduced and amplified. However cost, size, and other design considerations have generally dictated that electric instruments have a smaller number of electrical pickups than the number of strings on the instrument. Electric guitars and electric basses, for example, typically employ an elongated electric coil type pickup that spans the width of all four to twelve strings of the instrument, resulting in a composite signal that represents the vibration of all the strings. Such pickups are generally incapable of sensing the full range of harmonic tones generated by all of the strings. The result is that the pickup introduces its own qualities to the signal transduced from the vibrating strings, and as a result the sound reproduced by the loudspeaker is not a true representation of the acoustic properties of the instrument.
Electrical coil pickups are well known in the art. A coil pickup generally comprises one or more permanent magnets surrounded by a coil of wire. The magnet generates a magnetic field that passes through the pickup coil and also extends into the space occupied by the vibrating strings of the instrument. Vibration of the strings causes disturbances in the magnetic field which induce voltages within the surrounding coil. These voltages comprise the signal which is then amplified and broadcast over a loudspeaker. Thus, the pickup output signal does not actually relate directly to the motion of the strings, but rather, to the voltages induced in the coil. As a result, the sound reproduced by the loudspeaker will be affected by factors wholly unrelated to the acoustic characteristics of the instrument. Thus, the number of turns in the coil, the gauge of the wire comprising the coil, the number and position of the permanent magnets, and other factors will influence the sound of the instrument.
The sound of an electrical instrument is generally determined by the frequency response of the pickup. The pickups used today generally are high impedance devices designed to match the high input impedance of most amplifiers. That is to say, most pickups used today have an impedance in the range between 10K ohms and 60K ohms. Lower impedance pickups tend to have a good frequency response in the higher frequency ranges, but do not perform well at lower frequencies. On an electric guitar, these lower impedance pickups tend to work well when placed in the neck region of the guitar, but tend to produce a "tinny" sound when placed near the bridge. Conversely, pickups having an impedance greater than about 25K ohms tend to have excellent bass response but do not perform well in the higher frequency ranges. One less-than-satisfactory solution to this problem has been to provide a set of both higher and lower impedance pickups on the same guitar, and provide means for switching between the two, depending on the type of sound desired. Ideally a pickup would respond uniformly to all vibration frequencies of the instrument, but this is not possible with coil-magnet pickups due to limitations imposed by the laws of physics.
Another problem with magnetic coil pickups is that they tend to pick up electrical noise and interference signals from extraneous sources, such as power circuits, radio and television equipment, fluorescent lighting, and the like. Two-coil pickups, known as "humbuckers" were developed to reduce the amount of noise induced on a magnetic coil pickup. The "first generation" humbucker pickup actually comprises two coils spaced apart along the length of the strings. The coils are connected with opposite electrical polarities, so that the noise signals which are electrically induced in the coils are cancelled out. The two coils, however, are arranged so that the signals from the vibrating strings are added together. While the traditional humbucker pickup is effective in reducing noise, it has a drawback in that it senses string motion from two different points along the length of the string, approximately 0.6 inches apart. Thus, the signals from each coil which are added together are slightly out of phase. This poor phase relationship degrades the output signal so that it does not accurately represent the vibration of the strings.
Various designs such as a "stacked" humbacker where the two coils are wound onto the same armature but in opposite polarities, have been implemented in an attempt to combine the superior sound characteristics of a "single coil" pickup with the hum canceling characteristics of the traditional humbacker. However, none of these approaches can circumvent the physical laws that penalize the addition of a second coil. For example, the additional turns of wire of the second coil yield more inductance and capacitance which affect the tonality of the pickup. It simply has not been possible to construct a coil pickup that measures the true string movements of a guitar and reports those movements without coloration.
Other types of electrical pickups have also been used to transduce the vibration of musical instrument strings. Electromechanical vibration sensors of the piezoelectric, strain gauge and accelerometer type have also been used as pickups on musical instruments, primarily to amplify the sound of otherwise hollow-bodied acoustic instruments. However, such electromechanical transducers have not been completely effective in faithfully converting the vibrations of the instrument strings into electrical signals. This lack of fidelity is primarily due to the nature of the mechanical coupling between the vibrating string and the electromechanical sensor. Some of these couplings are quite complex and become quite expensive to manufacture. Furthermore, with electromechanical sensors, transients developed when the strings are actuated near the sensor tend to be overemphasized, and the pickups tend to be sensitive to body noises and body resonances when the resonating body reacts against the string-contacting transducer.
Another approach which has been employed with hollow-bodied guitars has been to mount a condenser microphone within the guitar. A desirable feature of this approach is that good condenser microphones are very accurate pressure transducers, and thus produce an accurate representation of the sound of the instrument. However, this approach is not well suited for concert situations where the microphone is also likely to pick up and amplify ambient sounds unrelated to the sound of the instrument itself.
Yet another method of sensing string vibration which has been employed is to detect minute electrical currents induced in electrically conductive strings when the strings vibrate in a magnetic field. However, the magnetic field required to induce detectable current signals within the strings has a downward pulling effect on the strings, which interferes with their natural resonance. While this approach may arguably produce a more accurate representation of string motion, the effective aperture is determined by the length of string exposed to the magnetic field. Due to the pulling effect of the magnets, it is desirable to minimize the magnetic aperture. However, small aperture and large output signal level are mutually exclusive, and this scheme has not become popular.
In light of the problems with the prior art, there exists a need for an improved electrical pickup for stringed musical instruments. It is desirable that a pickup be capable of individually transducing the vibration of only a single string, and that a plurality of such pickups be provided on a multi-stringed instrument, whereby the movement of each string may be separately transduced. Such a pickup could be produced with a sensor for each string on a harp, harpsichord, piano, dulcimer, or any other multistring instrument with ferromagnetic strings.
It is further desirable that the electrical signal output from such an improved electrical pickup be a true representation of the instantaneous position of a vibrating string, so that the sound of the instrument may be accurately reproduced without sonic colorations introduced by the pickup itself.
Ideally, an improved pickup will have a very small aperture, to produce a sensor that provides the truest rendition of string motion that includes all higher harmonics.
Finally, it is desirable to provide a musical instrument incorporating a plurality of such improved electrical pickups, at least one per string, whereby the output signal from each string may be individually manipulated so that selected sound characteristics may be purposely added to or removed from the signals.